1. Field of the Invention
This invention relates to a numerical control method and an apparatus thereof.
More specifically, this invention relates to a numerical control method and an apparatus thereof which have a circular interpolation locus display function for setting and adjusting servo parameters in order to use the most suitable servo characteristics in a machining process.
2. Description of the Related Art
Machine tools which execute three dimensional cutting or the like, have drive mechanisms which are arranged in each axis thereof, such as the X-axis, the Y-axis, and the Z-axis. A tool attached on a machine tool is simultaneously controlled by such drive mechanisms. As a result, more accurate three dimensional motion is made and three dimensional cutting, machining or the like, are executed.
A controller is used for these multi axes simultaneous control which uses a program control. This is a so called "numerical control apparatus (NC apparatus)".
Numerical control apparatus analyze a machining program which is externally input, and also analyze each command input in the machining program. Data for each axis are output in accordance with these commands, and a machining process is automatically executed. As a result, the machine tool, or the like, are controlled to have a desired motion.
Such an NC-device analyzes respective movement command values for the shafts from a predetermined movement command program input externally, and sequentially outputs the respective thus-analyzed command values into driving mechanisms for the corresponding shafts of the machine tool to thereby cause the respective driving mechanisms to cooperate and hence to cause the machine tool to automatically execute a desired operation set in the program.
If the machine tool executes a circular cutting motion, at least simultaneous two axis control is required. For example, when a real circle which as a radius r is described in the X-Y plane and the center of the circle has the coordinates (X.sub.0, Y.sub.0) in X-axis and Y-axis respectively, the X value and the Y value are controlled with cooperation in the expression: EQU (x-X.sub.0).sup.2 +(h-Y.sub.0).sup.2 =r.sup.2 ( 1)
Each axis value is simultaneously controlled according to: ##EQU1## When adjusting such simultaneous two axes control, if each servo characteristics is not adjusted well, an error occurs. The cutter path becomes different from the coordinates of a command value and the machining accuracy decreases.
There are many methods for servo adjustment, such as, gain adjustment, gain discrepancy adjustment between two axes, anticipation control, backlash compensation, and projection control or the like. These methods are used for adjusting the error corresponding to several error elements using the DBB measurement apparatus (Kakino et al. Study of the Motion Accuracy of NC Machine Tools (1st report)), Journal of The Japan Society of Precision Engineering, Vol. 52, July 1986 or the like, and these methods need expensive measurement tools and a high skill. An example of this is found in copending application Ser. No. 07/548,704, U.S. Pat. No. 5,189,627.
In another method, a circular cutting test is executed using a test piece, and the deviation of the circle from a perfect circle is measured by a circle perfection measurement apparatus. This method takes labor and time. Further, this method is effected by spindle rotation and a tool, so that it has not been estimated exactly.
Therefore, in the related art, such as DBB measurement apparatus or circular interpolation movement accuracy measurement method, much labor and time are needed. Thus, it has been desirable to provide an NC method and NC apparatus which are able to shorten the amount of labor and time for adjusting servo characteristic.